Vapor electric device



INVENTOR John L, Boyer. BY

fl flaw ATTORNEY J. L. BOYER VAPOR ELECTRIC DEVICE Filed June 30, 1949 Fig.l.

June 20, 1950 D. in Cm.

80 Pressure x Distance P. in mm. of Hg.

I! dill/Ill! I WITNESSES: WW 0 Patented June 20, 1950 UNITED STATES eA rgur-jforelegQ;

VAPOR ELECTRIC nEvioE I John L. Boyer; Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application June so, 1949, serial No. 1'0a2s4 1 4 Claims. (Cl. 250-275) My invention relates to a vapor electric device and particularly to a mercury arc device operating at high temperature and pressure.

In the operation of mercury are devices, the arc drop and electrode losses appear as heat. The maximum rating of thedevice is therefore determined by the ability to dissipate these losses.

Water and air-cooled tubes of the present design usually have temperature limits between 50 C. and 60 C. Since most rectifiers are re.- quired to operate with water or air temperatures up to 35 C., it is difficult to obtain sufficient cooling at higher ratings; Consequently, the necessity for a two-hour overload run at 150% of the rating usually determines the normal or states rating of the tube. Obviously, if'an increase of transfer of heat to the cooling medium could be increased, the rating of the tube could likewise be increased.

The important factor which limits the permissible temperature of the usual design of tubes, particularly of pool type tubes, is a rapid increase of the mercury vapor pressures with temperature so that the breakdown voltage decreases very rapidly with increase in temperature. As is well known, the breakdown pressure of mercury vapor has a typical so-called pressure distance curve, that is the distance in centimeters times the pressure in millimeters of mercury gives a pressure distance factor, and it is well known that at a very small pressure distance factor, the breakdown characteristic of mercury vapor is very high, and normal tubes are operative at a pressure distance factor of the order of 1 to 2 with a breakdown of several thousand volts. However, with increase in pressure or distance or both, the pressure distance factor rapidly increases and the breakdown voltage rapidly decreases so that in normal operating voltage a high rate of arc back occurs and prevents operation with a high vapor pressure distance ratio.

According to my invention, I provide a tube having long distances between the anode and any conducting surfaces at cathode potential so that the distance if of at least the order of 5 centimeters, and the pressure is increased by operating the tube at a temperature of the order of 200 C. to 300 C. so that a very high pressure is maintained in the tube. This high pressure times the line distance produces a very high pressure distance factor, and the tube operates on the outside end of the pressure distance curve so that again a very high breakdown characteristic is obtained. These high pressure tubes have a further advantage in that very simple internal structure permits a minimum of construction cost while the large quantity of vapor available permits the'carrying of large currents with a minimum of arc loss. Becauseof the simplicity of the interior structure'of the tube,' the arc drop also will be at a minimum. a

A further advantage lies the fact that as the tube operates at 'a' very high temperature the transfer of the arc and electrodelosses through the cooling mediumis much more easily accomplished, and large ratings can be satisfactorily cooled in relatively small cooling" surfaces,

When tub'esoperate at very low "pressures, sometimes thevapor available failsto carry the current and results in surging or momentary high voltages in the tubes or their associated circuits. With high pressure tubes,'a large quantity of vapor is available at all times to carry the current, and consequently little or no surging is to be expected. Further, because ofthe high current carrying capacity of the vapor, large overloads, even to short-'circuit,'may be carried without danger of damage to the tube."

It is accordingly an objectpf myinventi'on to provide a simplified tube" structure.

It is a further object of my invention to provide a mercury arc discharge device operating at high temperatures.

It is a further object of my invention to provide a mercury arc discharge device having high current characteristics.

Other objects and advantages of my invention will be apparent from the following detailed description taken in conjunction with the accompanying drawing, in which:

Figure 1 is a sectional elevation of a mercury arc device according to my invention; and

Fig. 2 is a diagrammatic presentation of a typical pressure distance breakdown curve.

In the exemplary embodiment of my invention, the vapor electric device comprises a metallic container I having a pool of mercury providing a mercury cathode 2 and cooperating with the mercury cathode is a suitable anode 3, preferably of graphite. The anode 3 and its stem 4 are widely spaced from all of the metallic or conducting surfaces of the container I so that the minimum distance from the anode 3 to any conducting surface .at cathode potential is at least of the order of 5 centimeters.

Suitable heating devices, herein shown as resistance type electric heaters 5, are provided around the body of the container 1 and are energized to maintain the temperature of the device of the order of 210 C. In order to facilitate vaporization of the mercury cathode, a suitable resistance heater 6 is preferably attached to the cathode plate I. By properly energizing these heating elements 5 and 6, a temperature of the order of 210 may easily be maintained, and a high mercury vapor pressure results.

In order to prevent condensation of mercury vapor on the anode3.or the rinsulating bushing 8, it is desirable to provide a heatingx'element 9 directly attached to the anode stem 4. In this manner the entire device will be maintained at? operating temperatures providing a high .vapor pressure, together with a high pressure distance characteristic.

Suitable cooling means should'. be-provided2forr dissipating the losses which occur in th-ertubes when operating at high load. Flor. this purpose I have shown a jacket l2 surrounding the tube f,

and a cooling fluid, such as air, may beacir'culalted characteristic may. bemaintained-witha very low pressure distance ratio, ittisz apparent that with alargedistance, such as .occurringsin gthe simple tube accordingsto. inyl invention. a.normally-very low: breakdown characteristic. could. be found. However, byheating-the containenl and the: merecury. thereintso that. a very;high.-pressureobtains a' pressure distance:characteristia having. arr in; verse breakdown.-.potentialor. substantially the same order as the: very, low pressure. distance characteristic.canbeobta-lnedr.

" said-anode being widely spaced from any conductingsurfa-ces at cathode potential and a heater '15:

supplyi g, heat to. said cathode material for maintainingzahiglr vapor pressure in said container.

2. Aheavy duty. vapor electric device comprising a container; a vaporizable reconstructing cathodein said container, an anode in said container, said anode being. spaced at least five centimeters frOm any conducting surfaces at cathode potential anda-.heating device formaintaining a vapor pressure-.ofathemrders ofrfortymm. of mercury.

31 A ,Vapor electric device comprising an evacuated container, ta quantity of; vaporizable, cathode material: in said-=containerg an anode in. spaced insulated: relation: in; said. container, heating means: maintaining-'awhigh vapor pressure in said container:

4'... Ar'vapor electric: arc discharge, device comprising: a". substantially evacuated container; an anode and at cathoderin said.- container, the parts of--said :devi'ce :which*'arexat' anode potentialibeing widely spacedfrom thepartszwhich' are :at cath ode potential; aquantity "of mercury in said" con:- taii-ier; heating -nreans for vaporizing said mercury to maintain: saididevice-operating in'a: high pressure distance region.

JOHN L. BOYER;

No references cited; 

